Method of preparing the double halide salts of thorium and alkali metals



United States Patent METHOD OF PREPARING THE DOUBLE HALIDE SALTS- OF THORIUM AND ALKALI METALS Samuel Z. Cardon, Euclid, Ohio, assignor, by mesne assignments, to the United States of America as representedrby'the United States Atomic Energy Commission No Drawing. Application November 4, 1953, Serial No. 390,269

6 Claims. (Cl. 23-145) This invention relates to a method of preparing the double halide salts of thorium and alkaliv metals, particularly the double chlorides. such. as NaThCls and KThCls.

Recently, a process has been developed for preparing thorium metal by the electrolysis of NaThCls. It is important, for the production of metal of useful purity which will have desirable characteristics of strength, ductility and other metallic properties, that the double salt be provided in substantially pure, anhydrous form and not in the form NaThCls-xHzO. The electrolysis referred to may be carried out. by passing a current through a fused mixture of the double salt and NaCl, at a temperature in the range of about 800ll F. Thorium metal so produced is useful for a number of purposes, such as in thorium coated. tungsten filaments in photoelectric cells, as the electrodes in glow discharge tubes, as the target in X ray tubes, in alloys of tungsten and thorium for making the filaments of incandescent electric lamps, for purposes where a source of radioactivity is needed, and as ajfertile material in nuclear reactors. of the breeder type.

Ordinary methods of preparing sodium thorium pentachloride lead to the formation of the hydrate. When attempts. are made todehydrate the latter, a difficulty is encountered in that there is a marked tendency to undergo an irreversible hydrolysis to metal oxide or oxychloride. Subsequently, when the double salt is used in electrolysis for producing thorium, these difiicultly decomposable hydrolysis products are found in the metal and they impair its purity and hence its physical properties. Conversely, if the double salt hydrate is employed in the electrolytic bath, at the high temperatures of the electrolysis, dehydration takes place attended by the same irreversible hydrolysis to produce the undesirable hydrolysis products.

Accordingly, it is an object of this invention to prepare anhydrous double chlorides of thorium and alkali metals, substantially free from impurities such as oxides and oxychlorides. Another object is to devise a method of preparing the double chlorides in which they are dehydrated and an irreversible hydrolysis to oxides and oxychlorides is avoided. Still another object is to devise a method of preparation of the double salts in which a step-wise method of temperature control is used to achieve the substantially pure, anhydrous salts. A further object is to prepare salts of the type indicated, useful as a starting material in a fused bath electrolytic process for preparing thorium metal.

It has now been found that these objects can be achieved by careful control of reaction conditions. Thus, in order to prepare NaThCl5, thorium carbonate or hydrated thorium tetrachloride is brought into contact with NaCl at a temperature in the range of 250-350 F. in the presence of NHiCl until reaction takes place to form the anhydrous salt. It has also been found advantageous to dissolve the thorium carbonate in concentrated HC], before further treatment. The function of the ammonium chloride is not completely understood but it is believed to assist in dehydrating the double salt formed. It is important to maintain the ammoniacal material present until the reaction is complete and. the water completely removed; and the temperature range of 250-350 F. used during this first stage of heating is. critical to avoid. the irreversible hydrolysis. A small amount of gaseousv ammoniacal products may occasionally be evolved during this step. When the reaction is completed and. the army drous double salt produced, heating may be continued to remove the remaining NH4C1 or its reaction or decomposition products, at higher temperatures if desired. The temperature for this second stage of heating is not particularly critical and may be in the range of. 300-1800 F. The temperature used is critical only so long as there is still physically or chemically bound water remaining, since above 350 F. this may result in the formation of the undesirable hydrolysis products. The method of this invention may also be applied to the preparation of other alkali metal-thorium double chlorides and fluorides whenever a similar difficulty is encountered in preparing the anhydrous double salt and avoiding hydrolysis. For: instance, it is known that elforts to dehydrate LiThCl5'8H2O lead to formation of the, oxychloride LiTh(OH)Cl4. In such instances the appropriate alkali metal compound will be used and the halogen of the halide compounds used will be chlorine or fluorine as may be appropriate for the particular double salt desired. The preferred procedure for obtaining the highest. purity NaThCls is to dissolve thorium carbonate in concentrated HCl and cause it to react with NaCl. and NHiCl at about 300 F. until the anhydrous double salt is formed, and then heat at 600 F. to remove rema'ming NH rCl or decomposition products thereof, more particularly as described in Example 1, following.

Example 1 ThOCOa is dissolved in concentrated HCl to give a clear yellow liquid. NaCl and NHiCl are then added tothis solution with vigorous stirring, The ratios used are ThOCO32 mols, NH4Cl'-2 mols, NaCl2.2 mol's and HCl-22 mols. This solution is then evaporated to near dryness during approximately 5 hours, at which point the mass is in semi-fluid form. Avoidance of overheating, i. e., above 350 F., is ensured by not exceeding semi-fluidity. The mixture is then placed in graphite crucibles, heated to 300 F. and held at that temperature for 2 hours. At the end of this time the product mixture appears as a porous, white microcrystalline material with a slight greenish yellow tinge. The temperature is then raised to 600 F. and held there for 14 hours. The mass is then allowed to cool, yielding a dense gray colored material. The resulting product is pure, anhydrous NaThCls. This is conveniently ground to a fine powder and stored in air-tight containers for use in the electrolytic preparation of thorium metal.

This example illustrates the following reaction:

To test the product qualitatively for the presence of oxychlorides, a sample is dissolved rapidly in hot water. The dissolving is done quickly since if it is digested for any length of time, the sodium thorium chloride starts to hydrolyze and the Whole mass precipitates out. If oxychloride is present, being insoluble, a flocculent white precipitate forms, or a milkiness appears if the amount is small. If a clear solution is formed, absence of the oxychloride is indicated. This test may also be applied to the reaction mass at any intermediate stage of preparation.

The NaThCls prepared by this example is reduced electrolytically to thorium metal. The metal analyzes approximately 99.0% thorium, 0.6% oxygen and 0.4%

, a 3 metallic impurities, these being chiefly iron and aluminum. This indicates that the oxygen content'due to oxychloride of the NaThCls, is less than 1%.

Example 2 In the dry state, one mol of thorium carbonate, four mols of ammonium chloride, and one mol of sodium chloride are mixed thoroughly together and are then disaggregated to fine particle size by passage of the'mixture through a micropulverizer. The mass is compressed and is heated at a temperature of 250 to 300 F. for 2 hours. Carbon dioxide and water vapor are evolved and some slight traces of ammonia. The reaction mass is allowed to cool to room temperature and two more mols of ammonium chloride are added. Again the mass is thoroughly comrninuted, and again compressed and is subsequently heated to 600 F. and held at that temperature for 14 hours. On cooling, a dense gray colored material is obtained corresponding to the compound NaThCls.

Example 3 A reaction mass consisting of one mol of thorium carbonate, four mols of ammonium chloride, and one mol of. sodium chloride is made as in Example 2 and heated as before to a temperature of 250 to 300 F. Anhydrous HCI gas is then introduced into the reaction mixture on a continuous basis during which the temperature is raised to=-600 F. and maintained at this temperature for 6 to 8lhours. On cooling, a dense gray colored material is obtained equivalent to the product NaThCls.

'i'Examples 2 and 3 illustrate'preparation in the dry state. If in the experiments described, a 2:1 ratio of NaCl to thorium carbonate is used instead of a 1:1 ratio, the product is NaZThCls.

Since many embodiments might be made of the present invention and since many changes might be made in the embodiment described, it is to be understood that the foregoing description is to be interpreted as illustrative only and not in a limiting sense.

' I claim:

. 1. The method of preparing alkali metal-thorium double halides in which the halogen is selected from the group consisting of chlorine and fluorine, which comprises the steps of heating a thorium compound selected from the group'consisting of the carbonate and the halides containing said halogen, with an alkali metal halide containing one of said halogens at a temperature in the range of 250350 F. and in the presence of the corresponding ammonium halide to produce the anhydrous double salt, and then heating the products to eliminate ammoniacal products. I

2. The method of preparing an alkali metal-thorium double chloride which comprises the steps of heating thorium carbonate with an alkali metal chloride in the presence of ammonium chloride at a temperature in the range of 250-350 F. to produce the anhydrous alkali metal-thorium double chloride, and heating the products further to eliminate ammoniacal products.

3. The method of preparing NaThCls which comprises the steps of heating thorium carbonate with sodium chloride and ammonium chloride at a temperature in the range of 250-350" F. to produce NaThCls, heating the products in the range of 300-1800 F. to eliminate ammoniacal substances, and recovering substantially pure NaThCls.

4. The method of preparing NaThCls which comprises the steps of heating thorium carbonate with sodium chloride in the presence of ammonium chloride at a temperature of about 300 F. to produce NaThCls, and then heating the products thus formed at about 600 F. to eliminate ammoniacal substances.

5. The method of preparing NaThCls which comprises the steps of dissolving thorium carbonate in concentrated H Cl, adding NaCl and NH4Cl and heating at a temperature in' the range of 250-350 F. until NaThCls is produced, and then heating at a temperature in the range of 300-1800" F. until ammoniacal products are no longer evolved.

6. The method of preparing NaThCls which comprises the steps of heating thorium chloride with sodium chloride and ammonium chloride at a temperature in the range of 250-350 F. until NaThCls is produced, and then heating the mass at a temperature in the range of 300-1800 F. to eliminate ammoniacal reaction products.

No references cited. 

1. THE METHOD OF PREPARING ALKALI METAL-THORIUM DOUBLE HALIDES IN WHICH THE HALOGEN IS SELECTED FROM THE GROUP CONSISTING OF CHLORINE AND FLUORINE, WHICH COMPRISES THE STEPS OF HEATING A THORIUM COMPOUND SELECTED FROM THE GROUP CONSISTING OF THE CARBONATE AND THE HALIDES CONTAINING SAID HALOGEN, WITH AN ALKALI METAL HALIDE CONTAINING ONE OF SAID HALOGENS AT A TEMPERATURE IN THE RANGE OF 250-350* F. AND IN THE PRESENCE OF THE CORRESPONDING AMMONIUM HALIDE TO PRODUCE THE ANHYDROUS DOUBLE SALT, AND THEN HEATING THE PRODUCTS TO ELIMINATE AMMONIACAL PRODUCTS. 